The present invention relates to a guide device, and more particularly, to a guide device or a linear bearing device for supporting an axially extending shaft member and a column slidable around the shaft member.
A linear guide is generally used for conveying products or articles in plants or factories. As shown in FIG. 11, a prior art linear guide 100 includes a linear rail 101 extending perpendicularly to the page, a slide base 102 provided over the rail 101, and a pair of tracking pulleys 104 each supported rotatably around a shaft 103 fitted to the bottom surface of the slide base 102. A linearly extending projection 101a of the rail 101 is engaged with a groove 104a formed around an outer circumferential surface of each tracking pulley 104.
In operation, when the slide base 102 slides along the extending direction of the rail 101, each tracking pulley 104 rotates around the shaft 103 and rolls along the projection 101a of the rail 101 with the groove 104a of the tracking pulley 104 engaged with the projection 101a of the rail 101.
In such a conventional linear guide, as shown in FIG. 12, a contact face between the groove 104a of the tracking pulley 104 and the projection 101a of the rail 101 is formed at positions where a distance from a center line of the tracking pulley 104, or a radius of the tracking pulley 104 is varied.
Thus, a circumferential speed of the tracking pulley 104 at a contact point having a radius of r1 differs from that of the tracking pulley 104 at another contact point having a radius of r2 ( greater than r1). Thus, when the tracking pulley 104 rolls along the projection 101a of the rail 101 and slides along the rail 101, a slippage will occur at positions where such a circumferential speed is different. As a result, the contact face between the groove 104a of the tracking pulley 104 and the projection 101a of the rail 101 will wear.
An object of the present invention is to prevent wear to the contact face of a guide device as well as to manufacture a slide base of a longer length as accurately as possible.
A guide device is provided to support a column or slide base having an axially extending shaft member thereinto to allow relative axial movement between the column and the shaft member. The column has an axially extending through hole or through groove. The shaft member penetrates the through hole or through groove of the column. A plurality of pockets are formed on an inner surface of the through hole or through groove of the column. The pockets are aligned on each of a plurality of cross sectional planes each perpendicular to the axial direction. In each pocket, there are provided a roller-shaped rolling element that rolls axially on an outer surface of the shaft member and a supporting shaft to support the rolling element rotatably. The column is formed of a plurality of splittable, disk-shaped members divided at the cross sectional planes that are perpendicular to the axial direction and that pass through the center line of the supporting shaft.
In this case, the rolling element that rolls axially on the outer surface of the shaft member has a roller shape or cylindrical shape, and the cylindrical surface forms a rolling surface. Therefore, a contact surface between the rolling element and the outer surface of the shaft member is formed at a position where a contact radius, or a distance from the center line of the rolling element is substantially constant. Thus, a differential slippage will not occur at a contact surface between the rolling element and the outer surface of the shaft member, thereby preventing wear to the contact surface between the rolling element and the outer surface of the shaft member.
Also, in this case, the whole column is formed of a plurality of splittable, disk-shaped members divided on the cross sectional planes each of which is perpendicular to the axial direction and passes the center line of the supporting shaft, thereby facilitating manufacture of a column of a longer length.
Generally, a column needs a boring or grooving process to form a through hole or through groove. However, when an integrated or one-piece column having a length of more than a certain length is bored or grooved, an actual boring or grooving process becomes difficult due to its length. Also, it increases a manufacturing cost to advance boring or grooving accuracy of such a column. On the other hand, according to the present invention, since a column is composed of a plurality of splittable, disk-shaped members stacked in the axial direction, boring or grooving each of the splittable members can be performed accurately by making each length of the splittable members a suitable length allowing for an accurate boring or grooving process. Also, combination of these splittable members suitably enables the whole column to extend as long as possible.
The shaft member may have a round outer circumferential surface and the rolling element may have a concavely curved cylindrical surface. Preferably, a radius of curvature xe2x80x9crxe2x80x9d of the cylindrical surface of the rolling element satisfies an inequality, 0.52Dxe2x89xa6rxe2x89xa60.58D, where D is a diameter of the outer circumferential surface of the shaft member.
In this case, the abovementioned relation increases a contact area of the rolling element with the outer circumferential surface of the shaft member, thereby decreasing surface pressure of the rolling surface. Thus, wear resistance can be advanced and an allowable load can be increased. Furthermore, smooth rotation of the rolling element is secured and skewing of the rolling element is prevented.
Additionally, in the case that a radius of curvature xe2x80x9crxe2x80x9d of a cylindrical surface of a rolling element is smaller than 0.52D, smooth rotation of the rolling element will be hindered and differential slippage will occur. On the other hand, in the case that a radius of curvature xe2x80x9crxe2x80x9d of a cylindrical surface of a rolling element is greater than 0.58D, a contact area becomes smaller and an allowable load will decrease.
Alternatively, the shaft member may have a flat outer surface extending in the axial direction and the rolling element may have a convexly curved or linearly extending generating line of a cylindrical surface. Thus, a smooth rotation of the rolling element can be secured and skewing of the rolling element can be prevented. Especially, in the case of the linear cylindrical surface, working of the rolling element becomes easy.
Each adjacent splittable member of the column is centered through the supporting shaft. Thus, additional parts are not required to center each splittable member, thereby decreasing the number of components and simplifying the structure of the device.
Preferably, each supporting hole for the supporting shaft is a blind hole without penetrating each of the splittable members axially and circumferentially. Similarly, each pocket is a blind hole without penetrating each of the splittable members axially and circumferentially. Thus, rigidity of each splittable member can be advanced.
A tubular member may be provided at an inner surface of the through hole or the through groove of each splittable member of the column in order to sustain an excessive radial load occurred between the shaft member and the column.